U.S. patent number 4,148,008 [Application Number 05/837,915] was granted by the patent office on 1979-04-03 for tire pressure monitoring system.
Invention is credited to Joe F. Lusk, William H. Rood.
United States Patent |
4,148,008 |
Lusk , et al. |
April 3, 1979 |
Tire pressure monitoring system
Abstract
A system for monitoring tire pressure preferably at each and
every tire to provide an indication of low, unsafe pressure to the
operator of the vehicle. The system can be used in pleasure
vehicles or commercial trucks and basically comprises a sensor unit
mounted to the tire rim including an actuating switch and coupling
coil, and a detector unit physically unattached to the sensor unit
and also including a coupling coil and associated detecting and
indicating circuitry. The sensor unit rotates with the tire and rim
while the detector unit, which is preferably mounted to the brake
shoe, is stationary enabling inductive coupling between sensor and
detector units once each revolution of the wheel of the vehicle.
The sensor unit is secured to the inner surface of the rim and is
compressable to operate the actuating switch. The detector unit may
be powered directly from the vehicle storage battery or may tie
into an existing diagnosis system of the vehicle.
Inventors: |
Lusk; Joe F. (W. Campton,
NH), Rood; William H. (W. Campton, NH) |
Family
ID: |
25275785 |
Appl.
No.: |
05/837,915 |
Filed: |
September 29, 1977 |
Current U.S.
Class: |
340/448;
200/61.25; 307/116; 340/521 |
Current CPC
Class: |
B60C
23/0428 (20130101); B60C 23/0498 (20130101) |
Current International
Class: |
B60C
23/04 (20060101); B60C 23/02 (20060101); B60C
023/02 (); G08B 023/00 () |
Field of
Search: |
;340/58,52F,646,675,676,517,521 ;200/61.22,61.25
;73/146.3,146.4,146.5 ;361/65,203 ;307/99,116,118 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell, Sr.; John W.
Assistant Examiner: Nowicki; Joseph E.
Attorney, Agent or Firm: Wolf, Greenfield & Sacks
Claims
What is claimed is:
1. A condition monitoring system comprising;
means for generating an alternating test signal,
first means including a monitoring switch means and first inductive
coupling means,
second inductive coupling means in periodic relative alignment and
with the first inductive coupling means,
means conveying the alternating test signal to the second inductive
coupling said test signal means including resistive means coupling
directly to the second inductive coupling means,
and means for sensing current flow through the second inductive
coupling means coupled from the resistive means and responsive to a
change in current flow through the resistive means,
whereby the condition of said switch means is determined by the
sensing of a low or negligible current when the switch means is
open and a reflected higher current when the switch means is
closed.
2. A system as set forth in claim 1 wherein said first means
includes a capacitance means forming, with said first inductive
coupling means, a tank circuit having a predetermined resonant
frequency so that when the switch means is closed a reflected
vibratory signal is induced in the second inductive coupling means
detected by the means for sensing.
3. A system as set forth in claim 2 wherein said means for sensing
includes means for sensing an amplitude change in the current flow
to said second inductive coupling means.
4. A system as set forth in claim 3 wherein said means conveying
the test signal defines a first path coupling to said second
inductive coupling means and said means for sensing is defined at
least in part by a second path including a charging capacitor and
at least one polarity detector.
5. A system as set forth in claim 4 including a load device coupled
to the first path so that the test signal may couple to both the
load device and the second inductive coupling means, said capacitor
being charged to one polarity upon failure of the load device and
to an opposite polarity upon closure of said switch means, further
including opposite polarity detectors for sensing the opposite
charged condition of said capacitor.
6. A system as set forth in claim 1 wherein the test signal is an
interrogation signal.
7. A system as set forth in claim 1 wherein the first and second
inductive coupling means comprise a transformer means having only
first and second inductors in voltage inducing relative
relationship.
8. A system as set forth in claim 7 wherein the resistive means
comprises a resistor and the sensing means detects changes in the
magnitude of current flow through the resistor.
9. A system as set forth in claim 8 wherein the sensing means
comprises a differential amplifier having its inputs coupled
directly across the resistor.
10. A system as set forth in claim 8 wherein the means for
conveying the test signal defines a first path, and further
including a second path to the sensing means, said first and second
paths conductively joining at said resistor and said sensing means
including a level detector.
11. A condition monitoring system comprising;
means for generating an alternating test signal,
first means including a monitoring switch means, first inductive
coupling means, and a capacitance means forming a tank circuit when
said switch means is closed, having a predetermined resonant
frequency,
second inductive coupling means in periodic relative alignment with
the first inductive coupling means,
a load device,
means defining a first path for conveying the alternating test
signal to both the load device and the second inductive coupling
means,
means defining a second path having a charging circuit and opposite
polarity detectors for sensing the opposite charge condition of the
charging circuit,
said charging circuit being charged to one polarity upon failure of
the load device and to an opposite polarity upon operation of said
switch means.
12. A system as set forth in claim 11 including unilateral
conducting means in the first path for passing only the opposite
polarity signals.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a system for monitoring the
pressure of tires on a vehicle, particularly a commercial vehicle
such as a tractor trailer. The invention is concerned with a
magnetic detection technique and employs a rotating sensor unit
cooperatively associated with a non-rotating detector unit.
There are a number of prior art systems for detecting the pressure
condition of vehicle tires. See for example, U.S. Pat. Nos.
3,831,161; 3,614,732; 3,665,387; 3,858,174; and 3,602,884. Of these
known systems there are certain disadvantages associated therewith
and it is one of the objects of this invention to provide an
improved system which overcomes many of these disadvantages. For
example, a system of the type shown in U.S. Pat. No. 3,602,884
requires modification of the tire rim. Also, this system mounts the
detection components outside of the wheel assembly and essentially
unprotected. Other prior art systems are rather complicated in
construction and still other systems are not readily adaptable to
any existing diagnosis system presently used with the vehicle. The
system of the present invention is particularly useful with a
diagnosis system of the type shown in U.S. Pat. No. 3,975,708.
Accordingly, one object of the present invention is to provide an
improved system for monitoring vehicle tire pressure employing an
improved form of magnetic coupling detection. In accordance with
the invention when tire pressure is sufficiently low, a resonant
condition exists, which condition is inductively coupled to
amplitude detection means.
Another object of the present invention is to provide a tire
pressure monitoring system that includes a sensor unit and a
detector unit physically unattached to the sensor unit and wherein
both units are mounted so as to be enclosed and thus protected from
dirt, grease, etc. In accordance with the invention the sensor unit
is secured to the inner surface of the tire rim in the space
provided between the rim and the tire itself. The detector unit is
secured to the brake shoe or the inner surface of the backing plate
so as to be substantially enclosed between the backing plate and
the brake drum.
A further object of the present invention is to provide a tire
pressure monitoring system that requires substantially no
alteration of the existing wheel system of the vehicle. In
accordance with the invention, rather than providing passages or
the like through the rim for receiving a transducer, the sensor
unit of this invention secured to the inner surface of the rim
without requiring any alteration to the rim.
Still another object of the present invention is to provide an
improved tire pressure monitoring system that is readily adaptable
for use with an existing diagnosis system presently in the
vehicle.
SUMMARY OF THE INVENTION
To accomplish the foregoing and other objects of this invention the
system comprises a first unit, herein termed a sensor unit
including a monitoring switch means and first inductive coupling
means. The sensor unit is mounted on the tire rim in the air
pressure space defined between the tire and rim and the unit is
rotatable with rotation of the tire. The system also comprises a
second unit, herein termed a detector unit, which is non-rotatable
essentially fixed in position in the vehicle. This detector unit
includes a second inductive coupling means and associated amplitude
detection means. The detector unit is preferably disposed in the
space defined between the brake drum and backing plate of the
vehicle wheel assembly so that the detector unit is protected from
any road hazards such as dirt and stones. The monitoring switch
means has a normal position which in the preferred embodiment is an
open position when the air pressure in the tire is above a
predetermined threshhold level. When the tire pressure decreases to
below this threshhold level, the monitoring switch means assumes a
second fault position, which in the preferred embodiment is a
closed position. The detector and sensor units are disposed in
relatively close proximity to each other; that is at least once per
revolution of the vehicle wheel. In this alignment position between
the units the amplitude detection means senses whether the
monitoring switch means is in its normal position or its fault
position. In the preferred embodiment the sensor unit comprises an
inductor and capacitor connected in a loop with the monitoring
switch means to thereby form a tank circuit. When the monitoring
switch means is opened, there is little or no inductive coupling to
the inductor of the detector unit but when the monitoring switch
means closes because of a fault condition, a resonance is
established and the change in amplitude of this signal at the
detector unit is sensed by the amplitude detection means to signal
the driver of the vehicle that a low tire pressure condition
exists.
In accordance with the present invention there is also provided an
improved construction of the sensor unit itself. The sensor unit
can be constructed quite compactly, and does not require any
modification of the tire rim. In the preferred construction the
sensor unit comprises an inductor and a capacitor coupled in a loop
with a monitoring switch. These components are contained within a
relatively rigid housing defining a space for the components and
also for a compressible medium such as a synthetic gel. There is a
rigid member associated with the sensor unit positioned for contact
with the movable portion of the monitoring switch. This rigid
member is arranged so that under no or low pressure conditions the
switch is in its closed position. When pressure is applied within
the tire against the exposed surface of the sensor unit, the rigid
member acts upon the monitoring switch to open its contacts thereby
opening the loop and establishing a steady state condition of
monitoring. When the pressure in the tire decreases the rigid
member relaxes and the switch is permitted to close thereby closing
the loop through the inductor and capacitor. This establishes a
resonant condition that is sensed by the detector unit during the
cooperative alignment between the unit.
DESCRIPTION OF THE DRAWINGS
Numerous other objects, features and advantages of the invention
should now become apparent upon a reading of the following detailed
description taken in conjunction with the accompanying drawings, in
which:
FIG. 1 is a cross-sectional view through one wheel of a vehicle
showing the physical arrangement of the components of the system of
this invention;
FIG. 2 is an enlarged cross-sectional view showing the detail of
the sensor unit of FIG. 1;
FIG. 3 is a schematic circuit diagram of one embodiment of the
present invention showing the detector unit and sensor unit;
and
FIG. 4 is another schematic circuit diagram of an alternate
embodiment of the invention as adapted for use with an existing
diagnosis system of the vehicle.
DETAILED DESCRIPTION
The system of the present invention is used to monitor tire
pressure and preferably includes means for monitoring the pressure
of each and every tire associated with the vehicle. The concepts of
the present invention may be employed with any type of motor
vehicle and other types of vehicles such as trailers. FIG. 1 is a
cross-sectional view showing a typical wheel assembly and the
arrangement of a portion of the system of this invention.
In FIG. 1 the wheel assembly includes a tire rim 10 upon which is
mounted the tire 12, brake drum 14, backing plate 16, and axle
housing 18. The axle itself has an end flange 20 to which the brake
drum and rim are secured in a conventional manner by bolts 21. The
axle housing 18 also has a flange 22 to which the backing plate 16
is secured usually by a bolting arrangement. The brake drum 14
rotates with the axle while the backing plate 16 is non-rotating.
FIG. 1 also shows the brake shoe 24 which is typically operated by
a wheel cylinder not shown in FIG. 1. The brake shoe 24 is
partially supported from the backing plate 16.
FIG. 1 shows the sensor unit 30 secured to the peripheral flange 32
of the rim 10. The complimentary detector unit 34 is secured to the
brake shoe 24 preferably on an inwardly facing surface thereof
opposite to the surface holding the lining of the brake shoe. The
spacing between the sensor unit and the detector unit is preferably
no greater than 7 inches when they are in relatively radial
alignment. The construction and position of the sensor unit 30 is
shown in more detail and discussed hereinafter with reference to
FIG. 2. Detector units are shown in FIGS. 3 and 4. The sensor unit
30 is totally contained in the space defined between the rim and
the tire. The detector unit 34 is contained in the enclosed space
35 defined between the backing plate 16 and the rotating brake drum
14. In this way the detector unit 34 is protected from any outside
hazards such as flying stones that would damage the detector unit
if it were located outside of the space 35.
FIG. 2 is a cross-sectional view of the sensor unit 30 shown
secured to the peripheral flange 32 of the rim. In FIG. 2 the
sensor unit 30 is shown in its compressed position with proper air
pressure in the space between the rim and tire being impressed upon
the unit primarily along the top surface 37 of the sensor unit.
Electrically, as also shown in the schematic diagram of FIG. 3, the
sensor unit 30 includes an inductor 38, a capacitor 40, and an
actuating switch 42. These components are intercoupled in a loop
which is encased in a compressible gel 44 contained within the
rigid plastic housing 46. The housing 46 includes a rigid leg 48
extending toward the actuating switch 42 for operating its movable
contact. In the position shown in FIG. 2 the rigid leg 48 is urged
against the movable contact so that the switch is in its open
position with the gel being compressed so as to permit the top wall
of the housing to move toward the actuating switch 42. Without any
pressure being applied to the surface 37 the rigid leg 48 moves
away from the switch 42 permitting its contacts to close. The
switch 42 is preferably of the type having an easily movable arm
that is normally biased to the closed position.
The sensor unit 30 has no connections that extend through the
flange 32, and is secured to the flange 32 in a suitable manner
such as by using an epoxy glue. In order to install the sensor unit
30 the tire is, of course, broken down to permit attachment of the
sensor unit to the rim.
The schematic diagram of FIG. 3 shows the sensor unit 30 which
comprises the inductor 38, capacitor 40 and actuating switch 42
interconnected in a loop. When the switch 42 is in its closed
position the circuit forms a tank circuit. In FIG. 3 it is noted
that one side of the inductor 38 is connected to ground. This
connection can be made quite easily by providing a separate
conductor wire in the embodiment of FIG. 2 coupled from the
inductor to the rim. Alternatively, the bottom wall of the housing
46 may be a conductive plate secured to the rim with a wire
connecting from the conductive plate to the inductor 38.
FIG. 3 also shows the detector unit 34 which may be encased in a
small housing and secured to the brake shoe as depicted in FIG. 1.
The detector unit includes a second inductor 39 which is grounded
on one side and connects on the other side to a sensing resistor R.
An oscillator is provided which may be a conventional design and
may be, for example, a 3 KHz oscillator. This oscillator is powered
from the +12 VDC line, which is the "hot" voltage normally
available in a motor vehicle. This voltage also couples to
transistor switch 50. A differential amplifier 52 couples across
the resistor R and senses a change in amplitude of the peak current
through the resistor R. The output of the differential amplifier 52
coules to the transistor switch 50.
Under normal operating conditions, with sufficient air pressure in
the tire, the switch 42 is in its open position as depicted in
FIGS. 2 and 3. Under that condition the secondary inductor 38 and
series connected capacitor 40 are open-circuited thus providing an
infinite impedance at the secondary coil 38 reflected as an
extremely high impedance to the primary circuit. The current
through resistor R is thus negligible and the output from the
differential amplifier 52 is insufficient to operate the transistor
switch 50. The coupling condition between the inductors 38 and 39,
of course, occurs only once each revolution of the tire when the
two inductors are in radial alignment.
When the air pressure drops below a predetermined threshhold level,
the switch 42 closes providing a closed loop circuit including the
inductor 38 and the capacitor 40 which together form a tank circuit
having a preselected peak resonant operating frequency preferably
selected at the operating frequency of 3 KHz. When the switch 42
closes, this resonant condition exists causing an induced
(reflected) low reactance in the primary coil 39 providing a
bipolar ringing signal having a relatively substantial peak
amplitude flowing through resistor R. This peak current or at least
one polarity thereof is sensed by the differential amplifier once
each revolution and as soon as the switch 42 has closed, the output
from the differential amplifier is of a sufficient magnitude to
cause actuation of the transistor switch 50. An alarm or indicator
means may be coupled from the transistor switch 50 to sense this
low tire pressure condition.
FIG. 4 shows another embodiment of the present invention used with
a diagnosis system such as shown in U.S. Pat. No. 3,975,708. This
prior art system employs a square wave generator such as the
generator 56 shown in FIG. 4 which, in the system arrangement,
couples to a number of different filter circuits for passing
different frequency signals to a number of different load devices
such as tail light lamps (one of which is shown in FIG. 4) for
sensing and indicating the condition thereof. In the embodiment of
FIG. 4 the indicating circuitry is essentially shared to detect two
conditions, (1) TL lamp out, and (2) tire pressure fault.
In FIG. 4 the square wave generator 56 is shown coupling to a
filter circuit comprised of inductor 58 and capacitor 60. The
values of these components may be chosen to pass frequencies about
100 KHz, for example. This cyclic frequency signal is coupled
through the filter circuit to the diode 62 and from there may
branch to either conductor path 63 or conductor path 64 both
depicted by arrows in FIG. 4. The conductor path 63 includes a
potentiometer 66, a capacitor 67 and a resistor 68. The path 64
couples by way of a resistor 70 and a diode 72 to either the
primary inductor 39 or lamp TL. It is noted in FIG. 4 that part of
the detector unit, namely the inductor 39, and the sensor unit 30
are substantially the same as shown in FIG. 3.
The embodiment of FIG. 4 operates on substantially the same
principles as the embodiment shown in FIG. 3. In FIG. 4 when the
tire pressure is at the proper levels, the switch 42 is open and a
primary winding 39 represents a substantially infinite impedance.
Even with this high impedance, however, the current flow is
predominantly down the path 64 because it is assumed that the lamp
TL is operating properly. Thus, under normal operating conditions
with the lamp operative and the switch 42 open, there is
insufficient current flow in the path 63 to substantially charge
capacitor 67. Under this condition neither of the bistable devices
76 or 80 are triggered. The bistable devices 76 and 80 may be
conventional devices and may even each be a comparator having the
input not shown in FIG. 4 coupled to the appropriate voltage so as
to sense positive and negative voltages. The device 76 detects a
positive voltage of a sufficient magnitude while the device 80
detects a negative voltage across capacitor 67 of a sufficient
magnitude.
Under the normal conditions previously expressed, the capacitor 67
does not charge sufficiently to trigger either of the devices 76 or
80. A signal from the generator 56 is selected to have a duty cycle
so that any charging of the capacitor 67 that occurs in a portion
of the cycle is followed by a discharge portion of the cycle that
never permits any appreciable total charging of the capacitor
67.
There are two fault conditions that could occur with the circuit of
FIG. 4. If the tail lamp TL comes open-circuited with the inductors
39 still representing an extremely high impedance then there is
virtually no current flow in the path 64. The burst of pulses from
the generator 56 is thus delivered to the path 63 causing a rapid
positive charging of capacitor 67. Almost immediately the device 76
is triggered and the triggering of this device is an indication of
the inoperability of the lamp TL.
Under the other fault condition, the switch 42 closes because the
tire pressure has been sufficiently reduced to cause this closing.
Under this condition there is essentially a tank circuit formed
with the inductor 38 and the capacitor 40 causing a reflected
signal in the primary inductor 39 which is in the form of a damped
ringing signal having both positive and negative peaks. The
negative peaks are essentially passed by way of path 64 through the
diode 72 causing a rapid negative charging of capacitor 67 which in
turn triggers the negative-responsive device 80. The positive
portion of the reflected signal was not coupled to the capacitor 67
because of the blocking provided by the presence of diode 72. Thus,
there is provided in FIG. 4 a unique circuit that has a capacitor
67 that receives either positive or negative charges for operating
the devices 76 and 80 depending upon a particular fault condition
that has occurred.
Having described a limited number of embodiments of the present
invention, it should now become apparent to those skilled in the
art that numerous other embodiments and modifications thereof are
contemplated as falling within the scope of this invention. For
example, in the disclosed embodiment the actuating switch 42 is
shown normally in an open position and is actuated to a closed
position by reduced tire pressure. In an alternate embodiment the
switch may be normally closed and moved to an open position for
detecting low tire pressure. Also, the detector unit 34 has been
shown secured to the brake shoe but also could be secured to the
backing plate or even the axle housing within the space 35.
* * * * *